The fabrication of fiber-reinforced polyester structures, such as boat hulls, by hand lay-up or spray-up of several layers of glass fiber/styrenated polyester composite over a form, called the "open mold" process, has been commercially practiced for many years. The open mold process is practical and relatively inexpensive for the fabrication of large fiber-reinforced polyester structures. However, the open mold process is disadvantageous in that significant amounts of volatile organic compounds escape into the ambient atmosphere creating environmental and health problems.
Recent legislation, in particular California's South Coast Air Quality Management District Rule 1162, restricts the amount of volatiles allowed to escape during the curing of fiber-reinforced polyester. The open mold process requires significant changes to comply with the new regulations. Specifically, the rule restricts volatile emissions to less than 60 g./m..sup.2 as measured by the Standard Method for Static Volatile Emissions (SCAQMD). Compliance with Rule 1162 may be achieved by (1) reducing the styrene content of the polyester resin formulation to less than 35 weight per cent, (2) substituting a lower-volatility monomer or comonomer mixture for the styrene or (3) using a suppressant.
Reduction of the styrene content in a polyester resin formulation to less than 35 per cent is disadvantageous for several reasons. Low-styrene formulations suffer from poor wetting characteristics and are difficult to apply to glass fiber reinforcements. Reduced styrene compositions for fiber-reinforced polyesters require the use of polyester oligomers of relatively low molecular weight in order to keep the system viscosity within a usable range, resulting in cured products of inferior physical properties.
Substituting a lower-volatility comonomer for all, or a portion, of the styrene is generally disadvantageous for economic and technological reasons. Substitution monomers such as vinyl toluene, alpha-methylstyrene or para-methylstyrene are generally more expensive than styrene. The substitution monomers yield resin formulations which are slow curing or suffer from incomplete curing under typical ambient curing conditions. Frequently the substitution monomers are not significantly less volatile than similar styrene-based formulations.
Current "suppressed" resin formulations also are disadvantageous. Typical commercial suppressants are wax based products. The was based products are of a limited compatability with the styrenated polyester resin. The wax based suppressants separate from the system during polymerization or curing, forming a surface layer which serves as a barrier to volatile emissions. The waxy surface layer must be removed prior to painting the fiber-reinforced polyester structure. Further, the weak, waxy layer left on the surface of the polyester resin by current suppressants results in poor secondary bonding characteristics for lamination applications.
It is desirable to lower the emissions of volatile compounds in the production of fiber-reinforced polyester products and to provide strong styrenated polyester resins.
It is an object of this invention to provide suppressants for unsaturated polyester resins, in particular, styrenated polyester resins. It is a further object to provide suppressants so that styrene or styrene/comonomer mixtures can be used at levels in excess of 35 percent of the total composition. It is another object of this invention to provide suppressants for styrenated polyester resins which are capable of being incorporated within the cured resin matrix. It is still another object of this invention is to provide suppressed styrenated polyester resin compositions which exhibit good bonding lamination characteristics and good glass wet-out characteristics.
These and other objects, together with the advantages over known methods shall become apparent from the specification which follows and are accomplished by the invention as hereinafter described and claimed.